1. Field of the Invention
The present invention relates to a magnetoresistive sensor sensitive for magnetic field, a magnetic head for reading information, which has been magnetically recorded, by the use of the magnetoresistive sensor as a read-back element, and a magnetic disk apparatus.
2. Related Art.
An improvement in the magnetic disk apparatus, in particular, in recording density of the magnetic disk apparatus is remarkable, and there have been demands for a high read output in a read-head which is a key device of the magnetic disk apparatus. In order to obtain a high read output in a high recording density, a gap between a magnetic recording disk and a magnetic head, head flying height, has become small. The current head flying height is approximately 30 nm, but it will be yet smaller hereafter, and it is expected that the magnetic head will be in a quasi-contact state in which it flies in an almost contact state with the magnetic recording disk or will be in a contact state in which it will really come into contact with the magnetic recording disk. In this case, it is thought that damage to the giant magnetoresistive (GMR) film occurs due to wear when a GMR film, which is a read-back element, is exposed to an air bearing surface of the magnetic head. As a technique for avoiding this trouble, for example, the magnetic head provided with a magnetic flux guide which extends towards a depth direction from the air bearing surface is disclosed in Japanese Patent Laid-Open No. 10-334418. In this magnetic head, a ferromagnetic layer (a free layer) of the GMR film whose magnetization direction changes in response to an external magnetic field is directly laminated on a part of the magnetic flux guide so that magnetization of the free layer is ferromagnetically coupled to that of the magnetic flux guide.
Additionally, a feasibility study has been also carried out for a high output in a magnetoresistive sensor film. Recently, a magnetoresistive (MR) head utilizing a magnetoresistive effect has been employed as the read-head. In the case of a recording density of several Gb/in2, the MR head utilizing an anisotropic magnetoresistive effect, AMR head, has been employed, however, the MR head utilizing a giant magnetoresistive effect, GMR head, is employed in the case of a higher recording density than it since the AMR effect lacks in sensitivity.
However, in order to further improve the recording density A hereafter, a still larger read output than the current one becomes necessary. For this end, research and development on a new magnetoresistive film superior to the GMR film has been actively carried out, and as one of the promising candidates, attention is paid to a ferromagnetic tunneling magnetoresistive (TMR) film in which a tunnel barrier layer is interposed between two ferromagnetic layers. With respect to the TMR film, for example, Journal of Magnetism and Magnetic Materials issued in 1995, vol.139, pp. L231 to L234 reported that a MR ratio of approximately 18% was obtained at room temperature in the constitution in which an Al oxide film was interposed between two Fe layers. Furthermore, Japanese Patent Laid-Open No. 3-154217 discloses the MR head employing the TMR film as the magnetoresistive sensor film.
Japanese Patent Laid-Open No. 10-334418 discloses the GMR head in which magnetization of a free layer is magnetically coupled to that of the magnetic flux guide by directly laminating the ferromagnetic layer (the free layer) of the GMR film, whose magnetization direction changes in response to an external magnetic field, on a part of the magnetic flux guide film. In this case, the magnetic coupling is ferromagnetic one. In this structure, magnetization of the magnetic flux guide rotates in response to a magnetic field from a medium, and thereby magnetization of the free layer ferromagnetically coupled to that of the magnetic flux guide also rotates, and the relative angle of magnetization to the ferromagnetic layer (a pinned layer) of the GMR film, whose magnetization direction is not changed by the external magnetic field, varies to generate resistance change. However, there is the problem that in the area of where the magnetic flux guide and the free layer are ferromagnetically coupled, which serve as the origin of the resistance change, magnetization rotation becomes difficult as compared with the area of the magnetic flux guide in which no free layer exists due to a large net magnetic moment, resulting in a lowering of sensitivity and difficulty with an improvement of the read output.
By the way, there are the problems to be solved in application of the TMR film to the MR head. The constitutions of the magnetoresistive sensor films for the MR head utilizing the AMR effect and the GMR effect are, for example, a transversal biasing layer/a nonmagnetic conductive layer/an AMR ferromagnetic layer and a free layer/a nonmagnetic conductive layer/a pinned layer/an antiferromagnetic layer respectively, and in general all the layers comprise the metal film. On the other hand, with respect to the TMR layer, the basic constitutions are a free layer/a tunnel barrier layer/a pinned layer, and among these, the tunnel barrier layer is a metal oxide layer with a thickness equal to several nm or less. It is necessary to fabricate the head so that the tunnel barrier layer does not short-circuit in the process for fabricating the head since the TMR is generated by a tunnel effect of electrons between the ferromagnetic layers via this tunnel barrier layer, and thus the technology peculiar to the TMR head, which is different from that of the conventional MR head, is required for the process for arranging and fabricating the longitudinal biasing layer for suppressing a Barkhausen noise of the free layer.
There is no description as to the longitudinal biasing layer, which is indispensable to a stable head motion, in the foregoing Journal of Magnetism and Magnetic Materials, vol.139, pp. L231 to L234 and Japanese Patent Laid-Open No. 3-154217.
Additionally, with respect to the AMR film and the GMR film currently used for the MR head, a sensing current flows in the in-plane direction of these films, on the other hand, with respect to the TMR film, the sensing current flows perpendicular to the film plane. Accordingly, there is the problem that resistance of the TMR element increases as the element size becomes small, resulting in increase in noise.
Furthermore, in the structure in which the magnetoresistive sensor film is exposed to the air bearing surface like that of the conventional MR head, there is also the problem that the two ferromagnetic layers which are arranged above and below the tunnel barrier layer respectively might short-circuit in a lapping processing of the air bearing surface, thus necessitating an extremely fine lapping technique.
Application of the structure disclosed in Japanese Patent Laid-Open No. 10-334418 to the TMR film allows the element size to enlarge, which makes it possible to reduce resistance of the element and there is no possibility for the short circuit since the barrier layer is not exposed to the air bearing surface. So it is thought that these problems can be overcome, but the problem still exists in the sensitivity decrease as described above.
Objects of the present invention is to improve sensitivity in the structure using the magnetic flux guide without exposing the magnetoresistive sensor films such as the GMR film and the TMR film to the air bearing surface, and to provide the magnetoresistive sensor having high sensitivity and high stability by applying the longitudinal biasing field to both of the magnetic flux guide and the free layer of the magnetoresistive film. Another object of the present invention is to provide the high-sensitivite magnetic head employing the magnetoresistive sensor having high sensitivity and high stability as the read-back element, and the magnetic disk apparatus with a high recording density, which mounts the same magnetic head.
In order to accomplish the above-mentioned objects, the present invention employs the structure of the magnetoresistive sensor described below. Firstly, to obtain high sensitivity, the structure was employed in which the magnetic flux guide for guiding leakage flux from a magnetic recording medium to the magnetoresistive sensor film was made to be antiferromagnetically coupled via a nonmagnetic intermediate layer to a fist ferromagnetic layer (the free layer or the layer in contact with a intermediate layer in case the free layer is the laminated structure), whose magnetization direction rotates in response to magnitude of the applied magnetic field, out of a plurality of the magnetic layers constituting the magnetoresistive sensor film. Furthermore, in order to realize high stability, the structure was employed in which the longitudinal biasing layer for suppressing a Barkhausen noise was provided for the magnetic flux guide. The antiferromagnetic coupling of the magnetic flux guide to the first ferromagnetic layer of the magnetoresistive film via the nonmagnetic intermediate layer allows the longitudinal biasing magnetic field, which has been applied to the magnetic flux guide, can be applied to the first ferromagnetic layer of the magnetoresistive sensor via the nonmagnetic intermediate layer.
Specifically, the magnetoresistive sensor in accordance with the present invention is characterized by comprising: the magnetoresistive sensor film having the ferromagnetic layer whose magnetization rotates in response to magnitude of the applied magnetic field; a pair of electrodes for flowing the signal sensing current to the magnetoresistive sensor film; and the magnetic flux guide for guiding the leakage flux from the magnetic recording medium to the magnetoresistive film, in which the ferromagnetic layer of the magnetoresistive sensor film whose magnetization rotates in response to magnitude of the applied magnetic field is antiferromagnetically coupled to the magnetic flux guide.
The magnetoresistive sensor film is arranged inside the element without being exposed to the air bearing surface and the magnetic flux guide whose end is exposed to the air bearing surface extends in the depth direction over the position of the magnetoresistive sensor film.
The magnetoresistive sensor in accordance with the present invention is characterized by comprising: the magnetoresistive sensor film having the ferromagnetic layer whose magnetization rotates in response to magnitude of the applied magnetic field; a pair of the electrodes for flowing the signal sensing current to the magnetoresistive sensor film; and the magnetic flux guide for guiding the leakage flux from the magnetic recording medium to the magnetoresistive sensor film, in which the ferromagnetic layer of the magnetoresistive sensor film whose magnetization rotates in response to magnitude of the applied magnetic field is antiferromagnetically coupled to the magnetic flux guide via the nonmagnetic intermediate layer made of Ru, Cr, Rh, Ir or alloys thereof.
A piece of the magnetic film can constitute the magnetic flux guide portion. Additionally, a first magnetic flux guide portion and a second magnetic flux guide portion can constitute the magnetic flux guide. In this case, the first magnetic flux and the second magnetic flux guide portions are made to be continuous from the air bearing surface into the depth direction, and to be magnetically connected at a position further from the air bearing surface than that of the magnetoresistive sensor film.
It is preferable to provide the longitudinal biasing layer for suppressing the Barkhausen noise for the magnetic flux guide. The longitudinal biasing field is substantially applied to the ferromagnetic layer, which is antiferromagnetically coupled to the magnetic flux guide by providing the longitudinal biasing layer for the magnetic flux guide for suppressing the Barkhausen noise.
The longitudinal biasing layer can be provided by laminating the magnetic flux guide thereon in the region or nearly the same region including its region, in which the ferromagnetic layer whose magnetization rotates in response to magnitude of the applied magnetic field is in contact with the magnetic flux guide via the nonmagnetic intermediate layer. Additionally, the longitudinal biasing layers can be provided for the both track-width-direction ends of the magnetic flux guide. In the case where the magnetic flux guide comprises the first magnetic flux guide portion and the second magnetic flux guide portion, the longitudinal biasing layer may be provided between the first magnetic flux guide portion and the second magnetic flux guide portion.
The magnetoresistive sensor film comprises the first ferromagnetic layer and the second ferromagnetic layer which have been laminated via the tunnel barrier layer and can be made to be such a type of the magnetoresistive sensor in which the magnetization of the first ferromagnetic layer rotates in response to magnitude of the applied magnetic field, the relative angle of the magnetization direction of the first ferromagnetic layer to the second ferromagnetic layer varies and thereby electric resistance changes. Magnetization of the first ferromagnetic layer rotates in response to magnitude of the applied magnetic field, and the magnetization direction of the first ferromagnetic layer is at a certain angle with the magnetization direction of the second ferromagnetic layer when the applied magnetic field is zero, and the relative angle of the magnetization direction of the first ferromagnetic layer to the second ferromagnetic layer varies and thereby electric resistance changes.
The magnetoresistive sensor film can be made to be such a type of the magnetoresistive sensor film in which at least two ferromagnetic layers are laminated at least once via the nonmagnetic conductive layer, the relative angle of the magnetization direction of the adjacent ferromagnetic layer via the nonmagnetic conductive layer varies and then electric resistance changes.
Additionally, the magnetoresistive sensor film can also be made to be such a type of the magnetoresistive sensor film in which the first ferromagnetic layer and the second ferromagnetic layer have been laminated via the nonmagnetic conductive layer, the magnetization of the first ferromagnetic layer rotates in response to magnitude of the applied magnetic field, the magnetization direction of the second ferromagnetic layer is pinned to nearly the depth direction, the magnetization direction of the first ferromagnetic layer is at a certain angle with the magnetization direction of the second ferromagnetic layer when the applied magnetic field is zero, and the relative angle of the magnetization direction of the first ferromagnetic layer to the second ferromagnetic layer varies and thereby electric resistance changes.
The magnetic head in accordance with the present invention is characterized by including the read-head which comprises: the magnetoresistive sensor film having the ferromagnetic layer whose magnetization rotates in response to magnitude of the applied magnetic field; a pair of the electrodes for flowing the signal sensing current to said magnetoresistive sensor film; and the magnetic flux guide which is antiferromagnetically coupled to the ferromagnetic layer of the magnetoresistive sensor film whose magnetization rotates in response to magnitude of the applied magnetic field and for guiding the leakage flux from the magnetic recording medium to the magnetoresistive sensor film.
The magnetic head in accordance with the present invention is also characterized by including a read-head which comprises: the magnetoresistive sensor film having the first ferromagnetic layer whose magnetization rotates in response to magnitude of the applied magnetic field and the second ferromagnetic layer, which have been laminated via the tunnel barrier layer; a pair of the electrodes for flowing the signal sensing current to the magnetoresistive sensor film; and the magnetic flux guide which is antiferromagnetically coupled to the first ferromagnetic layer of the magnetoresistive sensor film via the nonmagnetic intermediate layer made of Ru, Cr, Rh, Ir or alloys thereof and for guiding the leakage flux from the magnetic recording medium to the magnetoresistive sensor film.
The magnetic head in accordance with the present invention is also characterized by including a read-head which comprises: the magnetoresistive sensor film having the first ferromagnetic layer and the second ferromagnetic layer, which have been laminated via the nonmagnetic conductive layer, the magnetization of the first ferromagnetic layer rotating in response to magnitude of the applied magnetic field, in which a relative angle of the magnetization direction of the first ferromagnetic layer to the magnetization direction of the second ferromagnetic layer varies and thereby the electric resistance changes; a pair of electrodes for flowing a signal sensing current to the magnetoresistive sensor film; and a magnetic flux guide antiferromagnetically coupling to the first ferromagnetic layer of the magnetoresistive sensor film via a nonmagnetic intermediate layer made of Ru, Cr, Rh, Ir, or alloys thereof and for guiding leakage flux from the magnetic recording medium to the magnetoresistive sensor film.
The longitudinal biasing layer for suppressing the Barkhausen noise is preferably provided for the magnetic flux guide. The magnetic head also preferably comprises an inductive thin-film recording head as the recording head.
The magnetic disk apparatus in accordance with the present invention is characterized in that in a magnetic recording system comprising the magnetic recording medium, the magnetic head having a recording unit and a read-back unit, driving means for allowing the magnetic head to make a relative motion to the magnetic recording medium, and read/write signal processing means, the read-back unit of the magnetic head comprises: the magnetoresistive sensor film having the ferromagnetic layer whose magnetization rotates in response to magnitude of the applied magnetic field; a pair of the electrodes for flowing the signal sensing current to the magnetoresistive sensor film; and the magnetic flux guide which is antiferromagnetically coupled to the ferromagnetic layer of the magnetoresistive sensor film whose magnetization rotates in response to magnitude of the applied magnetic field and for guiding the leakage flux from the magnetic recording media to the magnetoresistive sensor film.
The magnetoresistive sensor in accordance with the present invention is also characterized by comprising: the magnetoresistive sensor film in which the first ferromagnetic layer, the nonmagnetic layer, the second ferromagnetic layer, and the antiferromagnetic layer are formed in order; a pair of the electrodes for flowing the signal sensing current to the magnetoresistive sensor film; and the magnetic flux guide for guiding the leakage flux from the magnetic recording medium to the magnetoresistive sensor film, in which the first ferromagnetic layer and the magnetic flux guide are formed via the nonmagnetic intermediate layer made of Ru, Cr, Rh, Ir or alloys thereof. The nonmagnetic layer can be made to be the tunnel barrier layer.
The magnetic head in accordance with the present invention is also characterized by comprising: the magnetoresistive sensor film in which the first ferromagnetic layer, the nonmagnetic layer, the second ferromagnetic layer, and the antiferromagnetic layer are formed in order; a pair of electrodes for flowing the signal sensing current to the magnetoresistive sensor film; the magnetic flux guide for guiding the leakage flux from the magnetic recording medium to the magnetoresistive sensor film; and the nonmagnetic intermediate layer made of Ru, Cr, Rh, Ir or alloys thereof, which is formed between the magnetic flux guide and the first ferromagnetic layer. The nonmagnetic layer can be made to be the tunnel barrier layer.